CN102111227B - Direct sequence (CDMA)/ (UWB)-based cognitive radio software simulation platform and designing method thereof - Google Patents

Abstract

The invention discloses a direct sequence code division multiple access (CDMA)/ultra wideband (UWB)-based cognitive radio software simulation platform, which consists of a source module, a UWB pulse generator module, a binary phase shift keying (BP SK) modulation module, a UWB channel module, an RAKE module, an equalizer module and a judging and error rate calculation module. The designing method of the platform comprises the following steps of: (1) inputting a Walsh sequences with the sequential values of +1, -1 and a bridge function sequence with the sequential values of +1, 0, -1, which serve as spectrum spreading sequences, into a simulation system; (2) inputting an m sequence and the bridge function sequence, which serve as the spectrum spreading sequences, into the simulation system; and (3) inputting a normal bridge function sequence and a bridge function intelligent code sequence, which serve as the spectrum spreading sequences, into the simulation system under a multi-user system.

Description

Based on cognitive radio software emulation platform and the method for designing thereof of direct sequence CDMA/UWB

Technical field:

The invention provides a kind of cognitive radio software emulation platform based on direct sequence CDMA/UWB, it is a kind of ultra wide band cognitive radio software emulation platform based on substrate formula (Underlay) access way.The cognitive radio communicatrion emulator of being built by MATLAB/SIMULINK, take Gaussian pulse as transmitted pulse, under the prerequisite being frequency expansion sequence with walsh sequence and bridge funcation sequence, can be judged by the calculating of the error rate, the three value bridge funcation sequences with zero correlation block have better bit error rate performance than walsh sequence.The invention belongs to cognitive radio technology field.

Background technology:

In nearest Two decades years, along with social development, the demand of people to radio communication increases sharply, and wireless network increases fast.Because many main wireless frequency spectrums have distributed to specific application, the rare of frequency spectrum becomes more and more serious.Therefore, under limited frequency spectrum resource, how to meet people's demand growing to radio communication is the very important and difficult task of wireless communication field one.Nearest test shows to authorize frequency spectrum not to be fully utilized.In this context, the radiotechnics that one class reuses frequency spectrum resource is proposed in succession by some research institutions and standards setting organizations, this is wherein most typical is the Technology of Ultra (U1traWideband, and cognitive radio technology (Cognitive Radio, CR) UWB).These two kinds of technology develop because of its tempting application prospect rapidly.And because they are in spectrum reuse mode, technology realizes many differences such as aspect, the further research novelty two kinds of technology combined is paid close attention to.

Super-broadband tech has started one research boom be applied to civil area from the nineties in last century after in the world, is considered to the revolutionary technology of next generation wireless communication.Ultra broadband, as a kind of wireless communication technology having a great difference with conventional art, has two-forty, low cost, the feature of low-power consumption, makes UWB become the optimal candidate technology of short distance high-rate wireless communication of future generation.Super-broadband tech can be divided into two classes at present: based on the impact class UWB of burst pulse formula and the carrier-class UWB based on modulated carrier spread spectrum formula.Correspondingly, UWB design in the highest flight comprises direct sequence CDMA/UWB scheme and multi-carrier OFDM/UWB scheme in the world at present.CDMA/UWB is the UWB scheme based on pulse, and OFDM/UWB is the UWB scheme based on multicarrier, and it adopts OFDM technology transmission sub-band information.Two kinds of technical schemes respectively have pluses and minuses.

Cognitive radio, as the revolutionary smart frequency spectrum technology of sharing of one, can improve the utilization rate of frequency spectrum significantly, receive the extensive concern of people in recent years.The concept of cognitive radio be the further expansion of software radio as a kind of brand-new intelligent wireless communication technology, it is more extensive that cognitive radio contains face, and the function of cognitive radio is also more powerful.

Bridge funcation system is a kind of non-sine orthogonal function system---bridge funcation system be made up of three values "-1 ", " 0 ", " 1 " element, shift parameters by means of it carrys out the ability of reconfigurable ability to interior sequences neutral element number and excellent anti-synchronous error, anti-multipath and multi-access inference, obtains increasing application.The reconfigurable ability of neutral element number that bridge funcation sequence has, allows it can adjust the length of code, the size of code collection and pattern according to the wireless environment of work.

The dynamic spectrum access technology of cognitive radio can be divided into interactive access (Overlay) and substrate formula access (Underlay).Specifically Overlay dynamic spectrum access is exactly that a cognitive nodes utilizes not by the one section of frequency spectrum access network used; The interference that this situation causes authorized user is minimum.This scheme of Underlay dynamic spectrum access make use of the spread of spectrum technologies of cellular network.Once obtain spectrum allocation may mapping graph (Channel Map, CM), cognitive nodes just starts transmission.On this section of frequency spectrum, authorized user processes the transmission of cognitive nodes as noise.Thus, this scheme needs complicated spread spectrum.Compared with Overlay frequency spectrum share scheme, this scheme can utilize wider bandwidth.

The present invention is fundamental simulation environment by MATLAB/SIMULINK, in Underlay mode for access technology, be send pulse with Gaussian pulse, with three value bridge funcation sequences for frequency expansion sequence, erect the software emulation platform based on ultra wide band cognitive radio, simulation result is contrasted as frequency expansion sequence by walsh sequence and the bridge funcation sequence with different zero correlation section length, simulation result shows, the three value bridge funcation sequences with zero correlation block have the ability than walsh sequence with better anti-multipath and multi-access inference, and the length of zero correlation block is longer, the ability of anti-multipath and multi-access inference is also stronger.

Summary of the invention:

The object of the invention is, a kind of cognitive radio software emulation platform based on direct sequence CDMA/UWB is provided, under this platform, can see from simulation result, by adopting different frequency expansion sequences, there are three value frequency expansion sequences of zero correlation block, there is than walsh sequence the ability of better anti-multipath jamming and anti-multi-access inference.

For achieving the above object, the present invention adopts following technical scheme:

A kind of cognitive radio software emulation platform based on direct sequence CDMA/UWB of the present invention, by Source module, UWB Pulse Generator module, BPSK Modulation module, UWB Channel module, RAKE module, Equalizer module, Judging and Error Rate Calculation module composition, as shown in Figure 1.

Wherein, Source module is signal source, is used for producing digital signal, primarily of Bernoulli Binary Generator module, and Product module and unipolar to bipolar converter module composition, as shown in Figure 2.BernoulliBinary Generator in this Source module generates random two and carries out information data 0 and 1 processed, and is turned into-1 and 1 by unipolar to bipolar converter.

Wherein, UWB Pulse Generator module is Gaussian pulse generator, in this module, and ultra broadband (UWB) pulse required for generation.Parameter that the cycle of pulse and bandwidth are defined by Workshop work station in MATLAB determines, and with bridge funcation sequence matrix optimized transmission waveform, and be input in scale operation module Gain, exported by wave form output end outWave module.Output waveform carries out BPSK modulation in BPSK Modulation module.BPSK modulation module is provided by MATLAB/SIMULINK software.Signal after modulation is sent in UWB Channel module.

Wherein, the standard ultra-wideband channel that UWB Channel module defines for IEEE802.15.3a, this module provides four kinds of standard ultra broadband (UWB) channel models that IEEE802.15.3a defines, is respectively CM1, CM2, CM3, CM4.Wherein CM1 is sighting distance type (LOS), channel model is the indoor environment of 0-4 rice, its excess-three kind channel is non line of sight type (NLOS), wherein CM2 is the indoor multipath channel model of 4-8 rice, CM3 is the indoor multipath channel model of 8-12 rice, and CM4 is outdoor channel model.In emulation platform constructed by us, UWB Channel module can be selected four kinds of channels.Wherein UWB Channel module is primarily of digital filter, and switching selector and logarithm white Gaussian noise generator composition, its structure chart as shown in Figure 4.After the UWB multipath channel that additive white Gaussian noise and logarithm normal distribution decline, output signal is the energy signal containing many different delay paths, and through RAKE module.

Wherein, what RAKE module adopted is PRAKE receiver, and select the suitable L paths arrived at first, merge by least-mean-square-error criterion, this RAKE module is provided by MATLAB/SIMULINK software.Then, in Equalizer module, recursive least-squares equalization algorithm is adopted to reduce the impact of multipath channel.

Wherein, Equalizer module is equalizer, is made up of one group of transversal filter, as shown in Figure 5, by four delay cells, and five taps and five adjustable complex multiplier (weights) compositions.The error rate is calculated by Judging and Error Rate Calculation module.Judging and Error Rate Calculation module is provided by MATLAB/SIMULINK software.

Wherein, BPSK Modulation module is BPSK modulation module

Wherein, Judging module is sampling judging module

Wherein, Error Rate Calculation module is error rate calculation module

A kind of method for designing based on the cognitive radio software emulation platform of direct sequence CDMA/UWB of the present invention, its step is as follows:

Step one, with sequential value for "+1 ", the walsh sequence of "-1 " and with sequential value for "+1 ", " 0 ", the bridge funcation sequence of "-1 " is input in constructed analogue system as frequency expansion sequence, and by changing the shift parameters j of bridge funcation sequence, to increase zero auto-correlation district of bridge funcation, can see from last the obtained simulation result of system and ber curve, the bridge funcation sequence with zero correlation block has better bit error rate performance than walsh sequence, namely has the ability of better anti-multipath jamming;

Step 2, m sequence and bridge funcation sequence are input in constructed analogue system as frequency expansion sequence respectively, can be seen by simulation result, when the zero correlation block of the smaller i.e. bridge funcation of bridge funcation shift parameters is smaller, adopt the system of m sequence slightly better than the ability of the system anti-multipath jamming adopting bridge funcation sequence, this is because the auto-correlation function of m sequence is a constant value except zero point, and closely 0, but along with the increase of bridge funcation shift parameters, namely when zero correlation is elongated gradually, bridge funcation sequence is adopted to have better bit error rate performance as the system of frequency expansion sequence,

Step 3, above step one and step 2 are it is considered that single user system suppresses the ability of multi-path jamming; Cross-correlation function is adopted to have the ability of bridge letter sequence as its suppression multi-access inference during frequency expansion sequence of zero correlation under present consideration multi-user system; We construct a ultra wide band cognitive radio system having two users to exist, making to have the bridge funcation sequence in zero cross-correlation district and the special cross-correlation function perseverance of a class is that the bridge funcation smart code sequence of 0 is as the frequency expansion sequence of system, simulation result shows, along with the increase of shift parameters, zero cross-correlation district is also increasing, system suppresses the ability of multi-access inference also more and more stronger, when adopting cross-correlation function perseverance to be the bridge funcation smart code sequence of 0, the bit error rate performance of system is best, namely suppresses the ability of multi-access inference to reach best.

Wherein, the bridge funcation sequence described in step one be combined by walsh function and Systems via Block Pulse Functions and the one that generates by " 1 ", "-1 ", the ternary sequence that " 0 " is formed, has obvious zero auto-correlation district and zero cross-correlation district.And determine zero auto-correlation district of bridge funcation and the length in zero cross-correlation district as the shift parameters j in bridge funcation, along with the increase of shift parameters j, the length of bridge funcation zero correlation block is also increasing gradually, and walsh function and Systems via Block Pulse Functions do not have similar character.And verified in a large amount of documents, the three value frequency expansion sequences containing zero correlation block significantly can reduce multi-path jamming.So in the simulation process adopted in step one, we have employed the bridge funcation sequence of different shift parameters and walsh sequence contrasts, along with the change of shift parameters, the length in zero auto-correlation district of bridge funcation is also increasing gradually, then the ability of system anti-multipath jamming is also more and more stronger.

Wherein, the m sequence described in step 2 is a kind of frequency expansion sequence widely used, its auto-correlation function except zero point place have kurtosis all the other some places external to be steady state values, and closely zero.When bridge funcation sequential shift parameter j is smaller, namely when the length in zero auto-correlation district is smaller, the ability of the anti-multipath jamming of bridge funcation sequence is not as m sequence, exactly because the auto-correlation function of m sequence is closely 0. when the shift parameters j of bridge funcation increases gradually, zero auto-correlation district increases gradually, and anti-multipath jamming ability strengthens naturally gradually.So when the bridge funcation sequence using zero correlation block larger, the ability of its anti-multipath jamming is better than m sequence.Under m sequence and the simultaneous situation of bridge funcation sequence, step 2 provides the criterion that is selected the better bridge funcation sequence of performance.

Wherein, in the multi-user system described in step 3, we have employed the system of two users.In this system, we have employed common bridge funcation sequence and the special bridge funcation sequence of a class and the bridge funcation smart code sequence frequency expansion sequence as system respectively.Numerous list of references is verified, and multi-access inference existing in multi-user system is determined by the cross-correlation function of frequency expansion sequence.In common bridge funcation sequence race, not homotactic cross-correlation function has obvious zero correlation block, can reduce the multi-access inference existed between multi-user.And the bridge funcation sequence that a class is special, namely its cross-correlation function perseverance of bridge funcation smart code sequence is 0.Can prove, when cross-correlation function perseverance is 0, the performance of best anti-multi-access inference should be had in theory.We use this kind of smart code sequence in the system of two users as frequency expansion sequence, simulation results show notional result, the system of smart code sequence is adopted to have better bit error rate performance than common bridge funcation sequence, the ability of namely more excellent anti-multi-access inference.

The present invention has following advantage and good effect:

1) the present invention constructs the cognitive radio software emulation platform of the employing Underlay access technology based on direct sequence CDMA/UWB.By adopting bridge funcation sequence as frequency expansion sequence, can verify that the ternary sequence with zero correlation block has the ability of better anti-multipath jamming than binary sequence.

2) cognitive radio system constructed by the present invention adopts a kind of special bridge funcation sequence and smart code sequence as frequency expansion sequence, and the cross-correlation function perseverance of this sequence is 0, effectively can strengthen the ability of the anti-multi-access inference of system.

3) method for designing is simple, and simulation velocity is fast, and result of use is good.

Accompanying drawing illustrates:

Fig. 1 is the single user software simulation system module frame chart of invention

Fig. 2 is Source function structure chart

Fig. 3 is UWB Pulse Generator function structure chart

Fig. 4 is UWB Channel function structure chart

Fig. 5 is Equalizer function structure chart

Fig. 6 is using walsh sequence and bridge funcation sequence as the contrast of single user system bit error rate performance during frequency expansion sequence

Fig. 7 is using m sequence and bridge funcation sequence as the contrast of single user system bit error rate performance during frequency expansion sequence

Fig. 8 is using common bridge funcation sequence as the bit error rate performance of multi-user system during frequency expansion sequence

Fig. 9 using a class special bridge funcation sequence and smart code sequence as follows as symbol description in the bit error rate performance figure of multi-user system during frequency expansion sequence:

In Fig. 1, Source module is signal source, is used for producing digital signal; UWB Pulse Generator module is Gaussian pulse generator; BPSK Modulation is BPSK modulation module; The standard ultra-wideband channel that UWB Channel defines for IEEE802.15.3a; RAKE module is PRAKE receiver; Equalizer module is equalizer; Judging is sampling judging module; Error Rate Calculation is error rate calculation module.

Fig. 2 is the structure chart of Source module.Source module and information data source module.Bernoulli Binary Generator and binary data generation module, Product is product calculation module.Unipolar to bipolar converter is dipole inversion module.Biploar is that reversed polarity exports, and Single is that former polarity exports.

Fig. 3 is UWB Pulse Generator function structure chart.Plus.PnWave is waveform generator.Signal FromWorkspace is the Wave data imported from MATLAB space.Gain is scale operation module.OutWave is output waveform end

Fig. 4 is UWB Channel function structure chart.Inl is input.Digital Filter is digital filter.WAGN is white Gaussian noise.IN/VarAWGN is logarithm white Gaussian noise and variance thereof.Channel.SNR is the signal to noise ratio parameter of channel.Switch is switching selector.Out2 is the output of UWB Channel module.

Fig. 5 is Equalizer function structure chart.Equalizer module is made up of one group of transversal filter, by four delay cells, and five taps and five adjustable complex multiplier (weights) compositions.Tbout is Equalizer module input, and Requa is Equalizer module output

Fig. 6 is the contrast of walsh sequence and bridge funcation sequence anti-multipath jamming ability.Smart code in I represents first kind bridge funcation smart code sequence.Because the ability of system anti-multipath jamming when what Fig. 2 and Fig. 3 compared is single user, and common bridge funcation sequence is identical with the character of first kind bridge funcation smart code sequence in zero auto-correlation district, so we adopt first kind bridge funcation smart code sequence to replace common bridge funcation sequence in single user situation.Abscissa Eb/No represents signal to noise ratio; Ordinate BitError Rate represents the error rate; J is the shift parameters of bridge funcation, and along with the increase of shift parameters, the zero correlation block of bridge funcation also increases gradually.

Fig. 7 is the contrast of m sequence and bridge funcation sequence anti-multipath jamming ability.Abscissa Eb/No represents signal to noise ratio; Ordinate Bit Error Rate represents the error rate; J is the shift parameters of bridge funcation, and along with the increase of shift parameters, the zero correlation block of bridge funcation also increases gradually.

Fig. 8 and Fig. 9 is that two users deposit error rate of system analogous diagram in case.The frequency expansion sequence adopted in Fig. 4 is common bridge funcation sequence, and the frequency expansion sequence adopted in Fig. 5 is special bridge funcation sequence, i.e. bridge funcation smart code sequence, and its cross-correlation function perseverance is 0.Abscissa Eb/No represents signal to noise ratio; Ordinate Bit Error Rate represents the error rate.

Embodiment:

A kind of cognitive radio software emulation platform based on direct sequence CDMA/UWB of the present invention, by Source module, UWB Pulse Generator module, BPSK Modulation module, UWB Channel module, RAKE module, Equalizer module, Judging and Error Rate Calculation module composition, as shown in Figure 1.

Wherein, Source module is signal source, is used for producing digital signal, primarily of Bernoulli Binary Generator module, and Product module and unipolar to bipolar converter module composition, as shown in Figure 2.BernoulliBinary Generator in this Source module generates random two and carries out information data 0 and 1 processed, and is turned into-1 and 1 by unipolar to bipolar converter.

Wherein, UWB Pulse Generator module is Gaussian pulse generator, in this module, and ultra broadband (UWB) pulse required for generation.Parameter that the cycle of pulse and bandwidth are defined by Workshop work station in MATLAB determines, and with bridge funcation sequence matrix optimized transmission waveform, and be input in scale operation module Gain, exported by wave form output end outWave module.Output waveform carries out BPSK modulation in BPSK Modulation module.BPSK modulation module is provided by MATLAB/SIMULINK software.Signal after modulation is sent in UWB Channel module.

Wherein, the standard ultra-wideband channel that UWB Channel module defines for IEEE802.15.3a, this module provides four kinds of standard ultra broadband (UWB) channel models that IEEE802.15.3a defines, is respectively CM1, CM2, CM3, CM4.Wherein CM1 is sighting distance type (LOS), channel model is the indoor environment of 0-4 rice, its excess-three kind channel is non line of sight type (NLOS), wherein CM2 is the indoor multipath channel model of 4-8 rice, CM3 is the indoor multipath channel model of 8-12 rice, and CM4 is outdoor channel model.In emulation platform constructed by us, UWB Channel module can be selected four kinds of channels.Wherein UWB Channel module is primarily of digital filter, and switching selector and logarithm white Gaussian noise generator composition, its structure chart as shown in Figure 4.After the UWB multipath channel that additive white Gaussian noise and logarithm normal distribution decline, output signal is the energy signal containing many different delay paths, and through RAKE module.

Wherein, what RAKE module adopted is PRAKE receiver, and select the suitable L paths arrived at first, merge by least-mean-square-error criterion, this RAKE module is provided by MATLAB/SIMULINK software.Then, in Equalizer module, recursive least-squares equalization algorithm is adopted to reduce the impact of multipath channel.

Wherein, Equalizer module is equalizer, is made up of one group of transversal filter, as shown in Figure 5, by four delay cells, and five taps and five adjustable complex multiplier (weights) compositions.The error rate is calculated by Judging and Error Rate Calculation module.Judging and Error Rate Calculation module is provided by MATLAB/SIMULINK software.

Wherein, BPSK Modulation module is BPSK modulation module

Wherein, Judging module is sampling judging module

Wherein, Error Rate Calculation module is error rate calculation module

A kind of method for designing based on the cognitive radio software emulation platform of direct sequence CDMA/UWB of the present invention, its step is as follows:

Step one, with sequential value for "+1 ", the walsh sequence of "-1 " and with sequential value for "+1 ", " 0 ", the bridge funcation sequence of "-1 " is input in constructed analogue system as frequency expansion sequence, and by changing the shift parameters j of bridge funcation sequence, to increase zero auto-correlation district of bridge funcation, can see from last the obtained simulation result of system and ber curve, the bridge funcation sequence with zero correlation block has better bit error rate performance than walsh sequence, namely has the ability of better anti-multipath jamming;

Step 2, m sequence and bridge funcation sequence are input in constructed analogue system as frequency expansion sequence respectively, can be seen by simulation result, when the zero correlation block of the smaller i.e. bridge funcation of bridge funcation shift parameters is smaller, adopt the system of m sequence slightly better than the ability of the system anti-multipath jamming adopting bridge funcation sequence, this is because the auto-correlation function of m sequence is a constant value except zero point, and closely 0, but along with the increase of bridge funcation shift parameters, namely when zero correlation block is elongated gradually, bridge funcation sequence is adopted to have better bit error rate performance as the system of frequency expansion sequence,

What step one and step 2 were considered is all single user system, specifically carries out in the following manner:

Single user DS-UWB system is discussed.In FIG, the Bernoulli Binary Generator in Data Source subsystem generates random two to carry out information data 0 and 1 processed and is turned into-1 and 1 by unipolar to bipolar converter module.In UWB pulse generator subsystem, produce Gaussian pulse waveforms.Output waveform carries out BPSK modulation in Data Modulation subsystem.Then signal transmission can be expressed as

$s\left(t\right)=\underset{n=-\∞}{\overset{\∞}{\mathrm{\Σ}}}{d}_{\left[\frac{n}{G}\right]}{c}_{n}p(t-n{T}_c)---\left(1\right)$

P (t) is normalization impulse waveform, and the duration is T _c; c _nthe spreading code of to be the cycle be G, symbol period is T _s=GT _c, therefore spreading gain is G.Modulation signal is sent to the ultra-wideband channel (SV/IEEE 802.15.3a) of standard

$h\left(t\right)=\underset{l=0}{\overset{L-1}{\mathrm{\Σ}}}\underset{k=0}{\overset{K-1}{\mathrm{\Σ}}}{\mathrm{\α}}_{k,l}(t-T_l-{\mathrm{\τ}}_{k,l})---\left(2\right)$

The wherein L number that is bunch, K is the number of bunch inner rays.α _{k, l}multipath gain, T _lthe time delay of l bunch, τ _{k, l}the relative time delay of kth article ray in l bunch. for convenience of derivation below, can reduced form in employing formula

$h\left(t\right)=\underset{l=0}{\overset{\mathrm{KL}-1}{\mathrm{\Σ}}}{\mathrm{\α}}_{l^{\′}}\mathrm{\δ}(t-{\mathrm{\τ}}_{l^{\′}})---\left(3\right)$

Easily find out l '=lK+k, α _{l '}=α _k, τ _{l '}=T _l+ τ _{k, l}received signal strength is

$r\left(t\right)=s\left(t\right)*h\left(t\right)+n\left(t\right)=\underset{l=0}{\overset{\mathrm{KL}-1}{\mathrm{\Σ}}}{\mathrm{\α}}_{l^{\′}}\underset{n=-\∞}{\overset{\∞}{\mathrm{\Σ}}}{d}_{\left[\frac{n}{G}\right]}{c}_{n}p(t-{\mathrm{\τ}}_{l^{\′}}-n{T}_c)+n\left(t\right)---\left(4\right)$

Received signal strength is the energy signal containing many different delay paths, adopt PRAKE receiver, select the suitable L paths arrived at first, merge by least-mean-square-error criterion, then, in Equalizer module, recursive least-squares equalization algorithm is adopted to reduce the impact of multipath channel.

Shift calculating onto through a series of, draw, the variance of multi-path jamming is

R _c(τ) be the autocorrelation of spreading code,

Finally, the error probability of the matched filter receiver synchronous with m article of multipath can be obtained according to BPSK BER formulas

$P_e=Q\left[\sqrt{\frac{{2E}_m}{{\mathrm{\σ}}_M{\mathrm{PI}}^2+N_0/2}}\right]---\left(6\right)$

E _mbe the received energy of the m article of each symbol of multipath, wherein

$Q\left(a\right)={\∫}_a^{\∞}\frac{1}{\sqrt{2\mathrm{\π}}}{e}^{-x^2}\mathrm{dx}---\left(7\right)$

By (5), (6). (7) formula comprehensively can obtain, because R _c(τ) be the autocorrelation for spreading code, because smart code sequence the increase of k value, zero correlation block is elongated gradually, and from (7) formula, bit error rate performance is become better and better. and Fig. 2,3 can well illustrate this problem.

Step 3, above step one and step 2 are it is considered that single user system suppresses the ability of multi-path jamming; Cross-correlation function is adopted to have the ability of bridge letter sequence as its suppression multi-access inference during frequency expansion sequence of zero correlation under present consideration multi-user system; We construct a ultra wide band cognitive radio system having two users to exist, making to have the bridge funcation sequence in zero cross-correlation district and the special cross-correlation function perseverance of a class is that the bridge funcation smart code sequence of 0 is as the frequency expansion sequence of system, simulation result shows, along with the increase of shift parameters, zero cross-correlation district is also increasing, system suppresses the ability of multi-access inference also more and more stronger, when adopting cross-correlation function perseverance to be the bridge funcation smart code sequence of 0, the bit error rate performance of system is best, namely suppresses the ability of multi-access inference to reach best.

Transmitter section and single user system similar, just many users, do not repeat them here, and now only consider receiver section.Specifically carry out in the following manner:

The acknowledge(ment) signal of receiver can be expressed as following form

$r\left(t\right)=\underset{k=1}{\overset{N_u}{\mathrm{\Σ}}}{s^{\left(k\right)}}_{\mathrm{rec}}\left(t\right)+n\left(t\right)---\left(8\right)$

Wherein n (t) is additive white Gaussian noise, N _uit is number of users

In a multi-path environment

$s_{\mathrm{rec}}^{\left(k\right)}\left(t\right)=\sqrt{E_p}\underset{j=-\∞}{\overset{\∞}{\mathrm{\Σ}}}\underset{n=0}{\overset{N_s-1}{\mathrm{\Σ}}}\underset{l=0}{\overset{L-1}{\mathrm{\Σ}}}{a}_l^{\left(k\right)}{d}_j^{\left(k\right)}{g}_n^{\left(k\right)}{w}_{\mathrm{rec}}(t^{\left(k\right)}-j{T}_f-n{T}_c-{\mathrm{\τ}}_l)---\left(9\right)$

Wherein E _ppulse energy, the channel coefficients of the 1st paths, multidiameter.

The template signal of the 1st correlator of P-Rake receiver can be written as following expression

Wherein the local pseudo random sequence produced, it is the channel estimating delay of the 1st paths

When signal is by L correlator, the expression formula of the signal of a kth user is

$r_l^{\left(k\right)}={\∫}_{{\mathrm{jT}}_f}^{{\mathrm{jT}}_f+(N_s-1)T_c}{s}_{\mathrm{rec}}^{\left(k\right)}\left(t\right)v\left(t\right)\mathrm{dt}$

Wherein it is the estimated value of weight estimator

The expression formula of kth user's multi-access inference is

Wherein σ _mAI=(R (Δ)) ²r _lk(τ) ²and R _lk(τ) be the cross-correlation function of frequency expansion sequence

After passing through L correlator, the expression of white Gaussian noise is

$n^2={\mathrm{\σ}}_n^2{N}_s^2{R}^2\left(0\right){\left(\underset{l=0}{\overset{L-1}{\mathrm{\Σ}}}{\mathrm{\γ}}_l\right)}^2---\left(13\right)$

Estimate according to standard gaussian, the expression formula of BER formulas can be written as

$P_e=Q\left[\sqrt{\frac{E_p{N}_S^2{R}^2\left(0\right){\left(\stackrel{L-1}{\underset{l=0}{\mathrm{\Σ}}{\mathrm{\γ}}_l{a}_l^k}\right)}^2}{E_p{N}_S^2{\mathrm{\σ}}_{\mathrm{MAI}}{\left(\underset{l=0}{\overset{L-1}{\mathrm{\Σ}}}{\mathrm{\γ}}_l{a}_l^{\left(k\right)}\right)}^2+{\mathrm{\σ}}_n^2{N}_S^2{r}^2\left(0\right){\left(\underset{l=0}{\overset{L-1}{\mathrm{\Σ}}}{\mathrm{\γ}}_l\right)}^2}}\right]---\left(14\right)$

Can be seen by formula (14), the cross-correlation function of frequency expansion sequence is less, and the bit error rate performance of system is better, and namely system suppresses the ability of multi-access inference also stronger.Fig. 4 and Fig. 5 contrast can well illustrate this problem.Fig. 4 is the bit error rate performance using common bridge funcation sequence as multi-user system during frequency expansion sequence.Fig. 5 is using the special bridge funcation sequence of a class and smart code sequence as the bit error rate performance of multi-user system during frequency expansion sequence.Contrasted can be obtained by two figure, adopt cross-correlation function perseverance be 0 bridge funcation smart code sequence than common bridge funcation sequence, there is better bit error rate performance, i.e. the ability of better anti-multi-access inference.

Claims (4)

1. the method for designing based on the cognitive radio software emulation platform of direct sequence CDMA/UWB, the method realizes based on the cognitive radio software emulation platform of CDMA/UWB, and this emulation platform is by Source module, UWB PulseGenerator module, BPSK Modulation module, UWB Channel module, RAKE module, Equalizer module, Judging and Error Rate Calculation module composition;

Described Source module is signal source, is used for producing digital signal, by Bernoulli Binary Generator module, Product module and unipolar to bipolar converter module composition; Bernoulli BinaryGenerator in this Source module generates random two and carries out information data 0 and 1 processed, and is turned into-1 and 1 by unipolar to bipolar converter;

This UWB Pulse Generator module described is Gaussian pulse generator, in this module, ultra broadband required for generation and UWB pulse, the parameter that the cycle of pulse and bandwidth are defined by Workshop work station in MATLAB determines, and with bridge funcation sequence matrix optimized transmission waveform, and be input in scale operation module Gain, exported by wave form output end outWave module; Output waveform carries out BPSK modulation in BPSK Modulation module; BPSK modulation module is provided by MATLAB/SIMULINK software; Signal after modulation is sent in UWB Channel module;

Tell the standard ultra-wideband channel that this UWB Channel module defines for IEEE802.15.3a, this module provides four kinds of standard ultra broadbands and UWB channel model that IEEE802.15.3a defines, be respectively CM1, CM2, CM3, CM4; Wherein CM1 is the i.e. LOS of sighting distance type, channel model is the indoor environment of 0-4 rice, and its excess-three kind channel is the i.e. NLOS of non line of sight type, and wherein CM2 is the indoor multipath channel model of 4-8 rice, CM3 is the indoor multipath channel model of 8-12 rice, and CM4 is outdoor channel model; In constructed emulation platform, UWB Channel module is selected four kinds of channels; Wherein UWB Channel module is primarily of digital filter, switching selector and logarithm white Gaussian noise generator composition, after the UWB multipath channel that additive white Gaussian noise and logarithm normal distribution decline, output signal is the energy signal containing many different delay paths, and through RAKE module;

What this RAKE module described adopted is PRAKE receiver, and select the suitable L paths arrived at first, merge by least-mean-square-error criterion, this RAKE module is provided by MATLAB/SIMULINK software; Then, in Equalizer module, recursive least-squares equalization algorithm is adopted to reduce the impact of multipath channel;

Described Equalizer module is equalizer, is made up of one group of transversal filter, by four delay cells, and five taps and five adjustable complex multipliers and weights composition; The error rate is calculated by Judging and Error Rate Calculation module; Judging and Error Rate Calculation module is provided by MATLAB/SIMULINK software;

It is characterized in that: the method for designing step of this emulation platform is as follows:

Step one, with sequential value for "+1 ", the walsh sequence of "-1 " and with sequential value for "+1 ", " 0 ", the bridge funcation sequence of "-1 " is input in constructed analogue system as frequency expansion sequence, and by changing the shift parameters j of bridge funcation sequence, to increase zero auto-correlation district of bridge funcation, see from last the obtained simulation result of system and ber curve, the bridge funcation sequence with zero correlation block has better bit error rate performance than walsh sequence, namely has the ability of better anti-multipath jamming;

Step 2, m sequence and bridge funcation sequence are input in constructed analogue system as frequency expansion sequence respectively, seen by simulation result, when the zero correlation block of the smaller i.e. bridge funcation of bridge funcation shift parameters is smaller, adopt the system of m sequence better than the ability of the system anti-multipath jamming adopting bridge funcation sequence, this is because the auto-correlation function of m sequence is a constant value except zero point, and closely 0, but along with the increase of bridge funcation shift parameters, namely when zero correlation block is elongated gradually, bridge funcation sequence is adopted to have better bit error rate performance as the system of frequency expansion sequence,

Step 3, above step one and step 2 are it is considered that single user system suppresses the ability of multi-path jamming; Cross-correlation function is adopted to have the ability of bridge letter sequence as its suppression multi-access inference during frequency expansion sequence of zero correlation block under present consideration multi-user system; Construct a ultra wide band cognitive radio system having two users to exist, making to have the bridge funcation sequence in zero cross-correlation district and the special cross-correlation function perseverance of a class is that the bridge funcation smart code sequence of 0 is as the frequency expansion sequence of system, simulation result shows, along with the increase of shift parameters, zero cross-correlation district is also increasing, system suppresses the ability of multi-access inference also more and more stronger, when adopting cross-correlation function perseverance to be the bridge funcation smart code sequence of 0, the bit error rate performance of system is best, namely suppresses the ability of multi-access inference to reach best.

2. the method for designing of the cognitive radio software emulation platform based on direct sequence CDMA/UWB according to claim 1, it is characterized in that: the bridge funcation sequence described in step one be combined by walsh function and Systems via Block Pulse Functions and the one that generates by " 1 ", "-1 ", the ternary sequence that " 0 " is formed, has obvious zero auto-correlation district and zero cross-correlation district; And determine zero auto-correlation district of bridge funcation and the length in zero cross-correlation district as the shift parameters j in bridge funcation, along with the increase of shift parameters j, the length of bridge funcation zero correlation block is also increasing gradually, and walsh function and Systems via Block Pulse Functions do not have similar character; The three value frequency expansion sequences containing zero correlation block can reduce multi-path jamming; So in the simulation process adopted in step one, the bridge funcation sequence and the walsh sequence that have employed different shift parameters contrast, along with the change of shift parameters, the length in zero auto-correlation district of bridge funcation is also increasing gradually, then the ability of system anti-multipath jamming is also more and more stronger.

3. the method for designing of the cognitive radio software emulation platform based on direct sequence CDMA/UWB according to claim 1, it is characterized in that: the m sequence described in step 2 is a kind of frequency expansion sequence widely used, its auto-correlation function except zero point place have kurtosis all the other some places external to be steady state values, and closely zero; When bridge funcation sequential shift parameter j is smaller, namely when the length in zero auto-correlation district is smaller, the ability of the anti-multipath jamming of bridge funcation sequence is not as m sequence, exactly because the auto-correlation function of m sequence is closely 0. when the shift parameters j of bridge funcation increases gradually, zero auto-correlation district increases gradually, and anti-multipath jamming ability strengthens naturally gradually; So when the bridge funcation sequence using zero correlation block larger, the ability of its anti-multipath jamming is better than m sequence; Under m sequence and the simultaneous situation of bridge funcation sequence, step 2 provides the criterion that is selected the better bridge funcation sequence of performance.

4. the method for designing of the cognitive radio software emulation platform based on direct sequence CDMA/UWB according to claim 1, is characterized in that: in the multi-user system described in step 3, have employed the system of two users; In this system, have employed common bridge funcation sequence and the special bridge funcation sequence of a class and the bridge funcation smart code sequence frequency expansion sequence as system respectively; Multi-access inference existing in multi-user system is determined by the cross-correlation function of frequency expansion sequence; In common bridge funcation sequence race, not homotactic cross-correlation function has obvious zero correlation block, reduces the multi-access inference existed between multi-user; And the bridge funcation sequence that a class is special, namely its cross-correlation function perseverance of bridge funcation smart code sequence is 0; When cross-correlation function perseverance is 0, the performance of best anti-multi-access inference should be had; This this kind of smart code sequence is used in the system of two users as frequency expansion sequence, simulation results show notional result, adopt the system of smart code sequence to have better bit error rate performance than common bridge funcation sequence, an ability of namely more excellent anti-multi-access inference.